Firearm with an expansion chamber with variable volume

ABSTRACT

Improvement to firearms suitable for utilization with different types of ammunition, in conditions of absolute safety, said firearm comprising an expansion chamber ( 10 ) that communicates with barrel ( 1 ) of the firearm through at least one connecting hole ( 14 ), a front and back calibration screw ( 13, 12 ), for increasing the volume available to the expansion of combustion gases. Said hollow expansion chamber ( 10 ) is located in the lower back part ( 9 ) of the barrel ( 1 ), (or possibly in its upper part, in parallel to it); said expansion chamber ( 10 ) being equipped with an internal threading ( 11 ) which is capable of engaging itself to back calibration screw ( 12 ) in the distal back part, and a further calibration screw ( 13 ), which can be manually operated by a threaded knob ( 13   a ), located in the front part.

DESCRIPTION

[0001] The present invention relates to the field of firearms, more particularly it is an improvement of the constructive technique of any type of firearms, like for example semiautomatic and not semiautomatic hunting rifles, military assault guns, machine guns, gunnery in general, as well as shotguns, to allow the employment of different types of ammunitions in absolutely safe conditions.

[0002] According to the present invention, a device to is provided which allows the user to increase or decrease as it suits him and according to the needs of the specific moment, the initial values of the pressure generated by the travelling charge (powder), following its ignition.

[0003] Since the pressure that builds up during gunpowder combustion is directly accountable for the speed which is given to the projectile, it is possible to adjust its speed and ensuing kinetic energy, in so doing varying the amount of energy given up to the target which is located at a certain distance.

[0004] In such a way it is advantageously possible to study new types of ammunitions (new calibres with particular amounts of propellent) with the aim of attaining a better quality from both the ballistics and the construction points of view.

[0005] It is known, from U.S. Pat. No. 3,381,403, a projecting unit for projecting a syringe projectile for administering of drugs, medicines and the like to animals.

[0006] This known apparatus is externally similar to a firearm such as a rifle or a pistol, but it is specifically designed to fire only explosive ballistic cartridge blank in order to provide propulsive power to a syringe projectile by means of a pre-expansion chamber.

[0007] The arrangement disclosed in U.S. Pat. No. 3,381,403 does not allow the use of different kind of a amunitions with a same firearm, but is only intended for the use of syringe projectiles having different weight with a same kind of blank cartridge.

[0008] It is also known, from FR 491.222, a device suitable for reducing the range of a gun or cannon (without varying the inclination of the barrel) by discharging a desired amount of the combustion gases, produced by the gunpowder combustion contained in the ammunitions, in the external environment. For this aim, FR 491.222 discloses a gun having a combustion gas discharging conduit that may be closed or opened by the user.

[0009] In this latter case, the discharged combustion gases are lost and they are not re-utilized for propelling the projectile.

[0010] The firearms known in the art were conceived and designed to endure and operate with explosive charges of a certain intensity, therefore the pressure that is generated employing ammunitions with the same calibre but with bigger charges is very dangerous as much higher pressure values are reached when compared with those that are expected at the designing stage. The “liveliness” of the powder and the limited volume available to combustion gases when they expand, a volume which is made available by the initial headway motion of the projectile, are concurring factors when pressure builds up to unacceptable values.

[0011] In these conditions, both the case and the weapon are mechanically strained, whereas the bullet receives a “ram blow”, which negatively affects its precision on the target.

[0012] Besides that, the mobile recoiling parts respond in such a way as to be factors that greatly increase the possibilities that structural failures occur in whatever weapon, with consequences that can be easily guessed, especially in machine-gun-type weapons, like said machine guns and military assault shotguns with a shooting range beyond 550-650 shots per minute.

[0013] It is well known that gunpowder has two important inherent features, the first being that the oxygen which is necessary for combustion to take place is intimately contained within the chemical formula of the gunpowder itself, therefore this can burn in the absence of air, that is in airtight environment (case), whereas the second feature which is even more important, is that the rate at which said combustion occurs is proportional to the pressure itself.

[0014] In other words, when the percussion has been triggered and it gives way to the beginning of the combustion of the charge contained in a case, the gas which is given off yields to a pressure increase around that charge which still has to burn. At this point the fundamental phenomenon because of which the powder reacts to yield a blast from being a simple combustion takes place.

[0015] This sudden pressure increase strongly accelerates combustion, with an ensuing production of further gas and a pressure increase, therefore a higher combustion rate.

[0016] Such a process is so fast that it seems to be instantaneous.

[0017] To understand the importance of the phenomena which have been described so far, it is enough to point out that an amount of gunpowder that only needs a couple of seconds to burn in the open air is consumed within a couple of thousandths of a second when it is compelled in a case.

[0018] Although very rapid, the combustion process described so far is the result of a sequence of events that can be controlled.

[0019] From the moment when the initiator lights the charge of a cartridge which is located in the chamber, the pressure starts to undergo a rapid increase, and the only “yielding” point within the blasting volume inside the case is the projectile, therefore compressed gases exert their propulsive action forcing the projectile out of the neck of the case and accelerating it along the muzzle (were the word “muzzle” is to be understood to include the entire barrel from the front end to the cartridge chamber to the exit).

[0020] Within this very limited time lapse, the best possible ratio must be attained between the rate of production of the gases that are given off by charge combustion and the rate at which the volume that they occupy increases when they expand.

[0021] It is essential to point out that the above volume is that given by the space between the bottom of the case and the base of the projectile. Therefore it linearly augments as the latter moves forward along the muzzle.

[0022] Therefore it is clear that the above ratio is extremely important and delicate.

[0023] If the charge burns too rapidly when combustion has just begun and the projectile has only travelled a short way along the muzzle, too much gas is produced and there is not enough space for its expansion to occur; this leads to an increase in pressure up to extremely high values that may even get to burst the breech of the gun.

[0024] From the safety point of view, the maximum pressure value is a very useful datum for an appraisal of how close a certain type of ammunition is to its failure limits or to those of a specific weapon

[0025] Nowadays, the employment of heavy ammunitions leads bullets to have higher initial speeds, tauter trajectories and greater kinetic energies, which means greater energies that can be given up, and increased penetration power.

[0026] One of the greatest problems of the prior art is given by the fact that free burst functioning with these heavy ammunitions would lead the weapon to undergo structural failures because of the excessive volume of gases produced during the explosion of the projectiles' charges.

[0027] Gas recovery systems are known in the art, but their only aim is that of expelling the exploded case so as to maintain the automatism in the functioning cycle of the weapon itself.

[0028] Since when smokeless gunpowder was discovered, that is more than a century ago, ammunition propellents have been manufactured thanks to techniques which developed with the objective to control combustion rate.

[0029] Therefore it is necessary to find a way to slow down the propellent combustion rate, accomplishing both a decrease in the initial pressure and a saving of part of the charge which is bound to burn later, consequently warranting a pressure which is suitable to the volume generated by the headway movement of the bullet along the muzzle.

[0030] Aim of present invention is that of increasing the volume made available to combustion gases following their expansion, by providing an expansion chamber whose volume can be adjusted.

[0031] In other words, according to the present invention, it is possible to adapt the physical features of the gun to the type of ammunition that is to be employed.

[0032] According to the invention, there is given a firearm which is equipped with a device, apt to adjust shot initial pressures, by dint of an ad hoc device which is calibrated to the millimeter range.

[0033] Such an adjustment device has a simple and rational shape, and it can be envisaged as substantially comprising three mechanical elements; an expansion chamber that communicates with the firearm muzzle through one connection hole at least, moreover a front and a back adjustment screws.

[0034] A better understanding of the features and advantages of the present invention can be gained from the following description, that refers to the attached drawings which illustrate a preferred embodiment of the present invention by way of a not limiting example.

[0035] In the drawings:

[0036]FIG. 1 schematically shows the very popular Soviet Automat-Kalashnikov assault gun;

[0037]FIG. 2 shows automatic gun shown in FIG. 1, which has been fitted (only by way of example) with the device object of the present invention;

[0038]FIG. 3 shows the same gun of FIG. 2, provided with a front guard;

[0039] In FIGS. 4A-4F there are schematically shown the several setting possibilities of the device according to the invention;

[0040] In FIG. 5 the expansion chamber and the assembly of its parts are shown;

[0041] In FIG. 6, a cross-section along the A-A plane of FIG. 5 is shown, and this highlights the fact that the muzzle and the expansion chamber form a welded monobloc;

[0042] In FIG. 7, a blown perspective view of the system is shown.

[0043] With reference to the figures, it ought to be observed that in the lower-back portion 9 of the muzzle, (or possibly in its upper part, in any case parallel to it), a hollow expansion chamber 10 is found to be located, said chamber being equipped with an inside threading 11. In its distal back part said threading hosts a clamping screw 12, whilst in its front portion 10, the chamber hosts a second adjustment screw 13, which can be manually operated by dint of a threaded knob 13 a located at its end.

[0044] The pitch of threading 11 is preferably in the millimeter range (that is one millimeter of axial movement for each full screw turn).

[0045] On shooting, a certain portion of the gases given off when combustion of the travelling charge of the cartridge takes place, is bled through one or more holes 14 (there are two of them in the embodiment shown), made in the area that connects the front end of the cartridge chamber with the beginning of the threading, corresponding to the contact area between the muzzle (1) and the chamber (10) area which is parallel to the longitudinal axis.

[0046] The optimal boring angle with respect to the muzzle axis is 90°.

[0047] Such gases are then conveyed towards the inside of the expansion chamber, compressing the air present inside it. Such an action yields pressures to be reduced to safety levels.

[0048] Pressure is reduced proportionally to the chamber's inner volume, therefore it results to be possible to optimally manage the energy produced by whatever charge load, even that of ammunitions whose charge was not conceived for a specific type of weapon, by simply adjusting screws 12 and 13, that are capable of varying the length and inner volume of the expansion chamber.

[0049] The sequence of events that characterise the phenomenon is shown as seen along an axial cross-section of the muzzle/device assembly in FIGS. 4A-4F.

[0050] The drawing of FIG. 4A shows the system as it appears when a cartridge is present in the chamber. By carrying out an adjustment so as to completely obstruct gas bleed holes 14, as shown in FIG. 4B (that is with the adjustment screw which is completely screwed in and is positioned in correspondence to the “0” mark of an ad hoc graduated scale), none of the gas given off by the shot is taken out of the chamber, therefore the internal ballistic features remain those of a traditional firearm.

[0051] Thus, the setting results to be optimal for a correct management of the energy produced by an ammunition characterised by normal charge loading.

[0052] In FIG. 4C, the projectile in its acceleration phase is shown, when it is about to reach the nearest or bleeding holes 14. At this stage the pressure is the closest to its highest values.

[0053] With the setting shown in FIG. 4D, that is with adjustment screw 13 set on the “10” mark of the graduated scale and both holes 14 open, when the projectile by-passes the bleeding holes, an optimal amount of the gases given off flows out of chamber 1, and reaches expansion chamber 10, in so doing causing the air cushion present inside it to be compressed.

[0054] Such a phenomenon prevents the gas pressure given by the employment of a high charge load cartridge from getting to its highest values that are excessive and would be rather harmful to both the weapon and the shooter.

[0055] The setting shown in FIG. 4E shows the adjustment screw set at the “20” mark in the graduated scale. In such a case, when the projectile by-passes bleeding holes 14, a different amount of the gases which have been given off flows out of muzzle 1 to reach expansion chamber 10 (with a greater capacity in comparison with the previous setting) and compresses the bulky air cushion present inside it.

[0056] Such a sequence ensures that even when the pressure that builds-up from a certain charge is extremely high, it does not reach the tremendous values that it would reach in the normal guns presently known in the art.

[0057] To get an idea of how important it is to control such pressures, it suffices to think that the real operating pressures normally reached by such cartridges are in the range of 3000-3500 atmospheres.

[0058] Finally, the setting shown in Fig. 4F highlights how back clamping screw 12 is also capable of accomplishing the obstruction of the nearest of holes 14, halving the flow rate of the gas that is bound to be conveyed into expansion chamber 10 underneath.

[0059] In order to do this, it is sufficient to screw in said back screw 12 until it reaches the position shown by reference number 26.

[0060] In conclusion it is worth noticing that screws 12 and 13 are advantageously equipped with their respective sealing rings 27 and 27A, which are made of heat enduring elastic material and accomplish their double aim of avoiding any possible pressure losses along the threading and of eliminating the even remote possibility of undesired unscrewings.

[0061] The present invention has been described and illustrated in terms of one of its preferred embodiments, but it is given for granted that whoever skilled in the art may make changes and amendments without stepping out of the scope of the present patent. 

1.) Device for increasing the volume of an expansion chamber for a firearm suitable to the employment of different types of ammunitions, in conditions of absolute safety, characterised by the fact that for increasing the volume available to the expansion of combustion gases, it provides for an expansion chamber (10) connected to muzzle (1) of the firearm through at least one connection hole (14) arranged near the beginning of the rifling, a front calibration screw (13) and a back calibration screw (12). 2.) Device according to claim 1, characterised by the fact that said hollow expansion chamber (10) is parallel to the muzzle and is located in the lower-back portion (9) of the muzzle (1), or possibly in its upper portion; said expansion chamber being equipped with an inside threading (11) capable of engaging itself with a clamping screw (12) in the distal back part, and a further registration screw (13), which can be operated manually by dint of a threaded knob (13 a), in the front part. 3.)Device according to the preceding claims, characterised by the fact that the threading (11) has a pitch in the millimeter range, that is there is a one millimeter long axial movement corresponding to each and every complete screw (13) turn. 4.) Device according to the preceding claims, characterised by the fact that to bleed a certain amount of the gases generated by the combustion of the travelling charge when the shot is fired, said holes (14) are made in the area that connects the front end of the chamber and the beginning of the rifling, corresponding to where the muzzle (1) is tangent to the chamber (10) parallel to the longitudinal axis. 5.) Device according to the preceding claims, characterised by the fact that the optimal angle between the axis (14) formed by the holes and the axis of the muzzle is 90°. 6.) Device according to the preceding claims, characterised by the fact that, being the reduction in pressure inside the chamber proportional to the inside volume of the expansion chamber (10), in order to attain an optimal regulation of the energy given off by any type of ammunition modifying the inside volume of the expansion chamber, are provided the screws (12) and (13) that are capable of changing the length of the chamber itself. 7.) Device according to the preceding claims, characterised by the fact that the back screw (12) and the front screw (13) are respectively equipped with rubber sealing material which endures heat, in correspondence of the inside ends of the expansion chamber, said sealing material being capable of preventing any pressure loss through the threading from occurring, it also being capable of avoiding any undesired unscrewings that would modify the volume of the expansion chamber (10). 